A storage device, such as a magnetic disc drive, stores user data and positional information on a recording medium that is divided into a large number of concentric tracks where each track is divided into data and servo sections. Positional information is stored within the servo sections and is read by a magnetic head. This position information includes a phase field, a track identification field, a sector identification filed and a position error field. The phase field is used to synchronize the frequency and phase of a demodulator used to demodulate the remaining fields including the position error field as well as to set an automatic gain control (AGC) for scaling the amplitude of the signal provided to the demodulator. The position error field is used to generate a position error signal, which provides an indication of the location of the magnetic head relative to a particular track center.
The positional information can be recorded on the storage medium by longitudinal recording or perpendicular recording. With longitudinal recording, magnetic fields containing bits of information are oriented longitudinally or parallel to the disc surface. With perpendicular recording, the magnetic fields are oriented perpendicular or normal to the disc surface so that bits of information are stored in an up or down orientation.
Perpendicular recording, although not currently shipped in products, is expected to provide advantages over longitudinal recording, especially as the data density of disc drives increases. However, it has been observed that at relatively large skew angles, perpendicular recording creates large variations in the position error signal.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.